Is going all catless on a na fa20 motor such a good idea?
 

I heard some motors need restriction in order to keep its power consistent. And eliminating some of these restrictions may even cause a decrease in power... Im no car genius but I'm assuming that the only way to get the best out of it is to switch to e85.. so what are your thoughts on the fa20 motor with nothing but 2.5 straight pipes.

I would also like to know if maybe even a tune for 93 oct would help...

And like I said before, I'm no car genius, that's why I'm asking this.

I thought the backpressure myth was busted.

Back pressure is never desireable but neither is having an exhaust pipe so big that the gasses lose too much velocity. Maintaining exhaust gas velocity as temp drops from entry to exit is what we really want to accomplish. You'll see that many oem exhaust systems use decreasing diameter pipe from front to back.

IMO 2.5" would work well enough although 2.25" would work equally well. Anything larger than 2.5" is strictly for FI. The biggest restrictions in the oem exhaust are the cats. I gained 25whp with just a Borla UEL, Tsudo hi-flo cat front pipe and a Visconti stage 2 tune. Replacing the rest of the exhaust probably wouldn't add much more than 5 more whp, if that.

Bingo. The ideal exhaust system would in theory have a constantly decreasing diameter with a few bends as possible. It would also have no restrictions such as cats present; which slow down the exhaust gas flow.

The ideal exhaust manifold has two diameters with an abrupt variation. It controls the pressure waves in the manifold and thus the acoustic effects affecting the engine's intake.

http://www.dailyicon.net/magazine/wp...1dailyicon.jpg

Now, on a street car, with an engine designed to run with cats, the valve timing has been set up to run with back pressure.
Losing the cats would help, but running with absolutely zero back pressure (i.e. too large decat pipes) on stock cam shafts and ECU would not give you better performance.

As a rule of thumb, modern catalytic converters lose very little power. The FA20 has lots more on left on the table than trading 1-ish HP for smelling like open ass every time you get out of the car.

For the sake of my own and everyone else's ears, please keep your cats on.

No one wants to hear a god awful raspy fartcan.

Honestly, the difference between cat and catless is negligible at best. One runs cleaner than the other and sounds MUCH better. Don't be a cheapass.

full catless will not only not net a benefit, but it will sound so raspy.

I am running a JDL Header, overpipe, Invidia catless midpipe and N1 and I have very little to no rasp at all. I know @nelsmar can attest to this as he was cruising next to me for a while on Saturday.

I thought for sure after the header install I would nee to go back to a catted frontpipe, but to me it sounds great without any cats.

I am going to try and get some good audio of it but I need something better than my phone

I am running Full catless with the Borla UEL and Perrin 3" catback exhaust... no rasp.. no fartcan.... all growl. Power seems fine... if i could only find where a dyno is around my area.

Rasp isn't necessarily caused by lack of cats guys. Add another resonator and the same effect of reducing rasp can be found. It has a lot to do with the frequencies that vibrate the materials. Also, shitty made mufflers can rasp with or without cats, and may only present the sound AFTER you go catless, i.e changing the frequency of the exhaust.

If you ever plan to autocross your car, you definitely want to keep a cat.

For environmental reasons you should keep your cats
Do you like the paint on your car? enough people remove their cats and we will have acid rain again

I heard that that setup was nice and very loud. Is yours really loud?

False.....


It does stink and it won't gain any power though, so no real good reason.